Rapidly dissolving granular hydrated calcium hypochlorite

ABSTRACT

A rapidly dissolving granular hydrated calcium hypochlorite product is comprised of hydrated calcium hypochlorite particles having at least 95 percent of the particles within a size range of from about 300 to about 850 microns. The product has a packed bulk density of less than about 1.05 grams per cubic centimeter. When dispersed on the surface of a body of water, such as a swimming pool, at least 3 feet deep, about 70 weight percent or higher of the particles dissolve within one minute.

This invention relates to calcium hypochlorite products used insanitizing applications. More specifically, this invention relates torapidly dissolving particles of hydrated calcium hypochlorite.

The use of calcium hypochlorite product in the sanitizing anddisinfection of water bodies is well known. Commercially employedgranular hydrated calcium hypochlorite particles of the prior art, whendispersed in water, for example, by casting or sprinkling the granularparticles on the surface of a swimming pool, dissolve somewhat slowlyand, in addition, leave undissolved particles as a residue on the bottomof the pool. This residue was found to be undissolved product which, inaddition to being unsightly, as it dissolves raises the pH in thedissolution zone and can result in promoting the precipitation ofcalcium carbonate, CaCO₃. Insoluble CaCO₃ particles require removal, forexample, by vacuuming the pool or by the filter system.

Among the properties which affect the solubility of calcium hypochloritein water are the particle size. It has been generally recognized thatthe particle size range is an important factor in the dissolving ratefor calcium hypochlorite. For example, U.S. Pat. No. 2,693,454,published Nov. 2, 1954, by E. C. Soule teaches that quick dissolving,quick acting and non-sludging bleach mixtures are obtained using, as oneingredient, anhydrous calcium hypochlorite having an available chlorineconcentration upwards of 60 percent and a water content not over about 2percent in a semi-granular form. The particles should pass a 30 meshscreen and remain as a 60 mesh screen and not contain more than about 20percent of fines which pass a 100 mesh screen.

H. L. Robson, in U.S. Pat. No. 2,959,554, Nov. 8, 1960 describes bleachsolutions containing anhydrous calcium hypochlorite having an availablechlorine content of 70 to 76 percent in granular form which passesthrough a 30 mesh and is retained on a 70 mesh screen, with the weightpercent passing a 100 mesh screen should not exceed 10 to 12 percent andthe weight coarser than 30 mesh should be less than 5 percent.

The screen analyses for anhydrous calcium hypochlorite containing about70 percent available chlorine employed in the bleaching compositions ofA. Long et al in U.S. Pat. No. 3,639,284 is as follows:

    ______________________________________                                        Screen           Granular                                                     ______________________________________                                        On 16 mesh       8                                                            On 20 mesh       35                                                           On 30 mesh       33                                                           On 40 mesh       16                                                           On 50 mesh       5                                                            On 70 mesh       1.3                                                          On 100 mesh      --                                                           Through 70 mesh  1.7                                                          Through 100 mesh --                                                           Total            100.0                                                        ______________________________________                                    

The bulk density of the commercial anhydrous calcium hypochloritegranules employed by Long et al had a minimum (loose packed) density ofabout 0.79 and a maximum (shaken) density of about 0.83.

Hydrated calcium hypochlorite particles may be produced by knownprocesses such as those described in U.S. Pat. No. 3,544,267 issued onDec. 1, 1970, to G. R. Dychdala or U.S. Pat. No. 3,669,894 issued onJune 13, 1972, to J. P. Faust.

Particles of solid, hydrated calcium hypochlorite products produced bycommercial processes contain from about 55 to about 75 percent andpreferably from about 65 to about 72 percent by weight of calciumhypochlorite Ca(OCl)₂, and from about 4 to about 10 percent andpreferably from about 5 to about 8 percent by weight of water, thebalance being inert materials usually resulting from the process ofmanufacture, e.g. sodium chloride, calcium hydroxide, calcium chlorideand calcium carbonate.

The hydrated calcium hypochlorite particles produced in any commercialprocess are then separated to provide particles having a selected sizerange. Any suitable separation method may be used including, forexample, screening and air classification. In the separation process,the oversized particles are reduced in size, for example, by crushing,and the undersized particles are compacted. Both the crushed particlesand the compacted particles are fed back through the separationapparatus along with additional particles of hydrated Ca(OCl)₂ from thecommercial process.

The dissolving rate of the above calcium hypochlorite compositions,however, is not sufficiently fast when dispersed on the surface of awater body such as a swimming pool to prevent the accumulation ofundissolved materials on the bottom.

It is an object of the present invention to provide a granular hydratedcalcium hypochlorite which dissolves rapidly in water and, whendissolved, leaves reduced amounts of undissolved material.

This and other objects of the invention are accomplished by a rapidlydissolving granular hydrated calcium hypochlorite product comprised ofhydrated calcium hypochlorite particles having at least 95 percent ofsaid particles within a size range of from about 300 to about 850microns.

More in detail, the novel granular product of the present invention iscomprised of hydrated calcium hypochlorite particles having a selectedparticle size range which rapidly dissolve when dispersed in a swimmingpool and substantially reduce the amount of undissolved product on thebottom of the pool. The product is obtained by the separation ofcommercially produced hydrated calcium hypochlorite on at least twoscreens. The first screen retains particles greater than about 850microns and passes particles equal to or smaller than about 850,preferably smaller than 800 microns. The larger particles are fed to acrushing device and the size reduced. Hydrated calcium hypochloriteparticles 850 microns or less in size are passed to a second screenwhich retains particles larger than about 300, preferably larger thanabout 350 microns. Suitably, the particle size range for the granularhydrated calcium hypochlorite product of the present invention has atleast 95%, preferably at least 97%, and more preferably at least 98% ofthe particles within the size range of from about 300 to about 850microns. The selection of this particle size range for hydrated calciumhypochlorite surprisingly results in a reduced quantity of undersizedparticles and a subsequent reduction of the amount of hydrated calciumhypochlorite which must be compacted. Lowering the amount of compactedhydrated calcium hypochlorite particles results in a faster dissolvingproduct. The presence of compacted material is reflected by an increasein the packed bulk density. Suitably the packed bulk density of theproduct of the present invention is less than about 1.05, for examplefrom about 0.90 to about 1.03, and preferably from about 0.95 to about1.02 grams per cubic centimeter as determined by the method of paragraph4.3.7 in Federal Specification 0-C-114 B, Amendment-2, Mar. 9, 1977entitled Calcium Hypochlorite, Technical. When added to a body of watersuch as a swimming pool, the novel granular hydrated calciumhypochlorite product of the present invention dissolves rapidly andresults in a substantial reduction in the amount of undissolved productwhich reaches the bottom of the pool. For example, when the product ofthe present invention is dispersed on the surface of a water body atleast 3 feet deep, at least about 70 and preferably about 72 percent byweight of the particles dissolve within one minute.

The novel product of the present invention is further illustrated by thefollowing examples. All parts and percentages are by weight unlessotherwise specified.

EXAMPLES 1-4

Granular hydrated calcium hypochlorite particles having reduced amountsof compacted material were passed through a controlled screeningprocess. The hydrated calcium hypochlorite products recovered had thefollowing composition and particle size range, each example representsthe average product produced daily for the period of one month.

    ______________________________________                                                      Exam-  Exam-   Exam-   Exam-                                                  ple 1  ple 2   ple 3   ple 4                                    ______________________________________                                        Average Ca(OCl).sub.2                                                         Composition                                                                   % Ca(OCl).sub.2 70.33    69.70   69.64 69.09                                  Total Alkali    3.59     3.36    3.41  3.60                                   % CaCl.sub.2    0.43     0.84    0.70  0.89                                   % NaCl          16.75    16.58   15.66 16.65                                  % Ca(ClO.sub.3).sub.2                                                                         1.34     1.13    1.25  1.35                                   % CaCO.sub.3    2.39     1.93    2.34  2.42                                   Packed bulk Density (g/cc)                                                                    1.01     1.03    1.00  1.00                                   % Screen Analysis                                                             Mesh     Microns                                                              +20      >850       0.16     0.17  0.18  0.21                                 -20 to +50                                                                             850 to 300 98.55    98.67 98.51 98.08                                -50      <300       1.39     1.19  1.29  1.33                                 ______________________________________                                    

Five grams of the granular hydrated calcium hypochlorite product havinga known available chlorine concentration were placed on the surface of atank of water four feet deep. No circulation or agitation was presentduring the initial dissolution period. The granular hydrated calciumhypochlorite particles passed through the water for a period of oneminute. At the end of this period, any undissolved particles wereremoved from the bottom of the tank. A pump was operated for fiveminutes to provide a homogeneous solution. The available chlorineconcentration of this solution was then determined and the percentage ofthe product dissolved was calculated. For each example, this procedurewas repeated daily for one month. The average percent of improvedhydrated Ca(OCl)₂ particles dissolved is given in Table I below.

COMPARATIVE EXAMPLES A, B, C, and D

Commercial granular hydrated calcium hypochlorite particles wereproduced during the same time periods as those of Examples 1-4 havingthe following average compositions and sieve analysis:

    __________________________________________________________________________                  Comparative                                                                          Comparative                                                                          Comparative                                                                          Comparative                                              Example A                                                                            Example B                                                                            Example C                                                                            Example D                                  __________________________________________________________________________    Average Ca(OCl).sub.2                                                         Composition                                                                   % Ca(OCl).sub.2                                                                             69.57  69.18  68.94  68.61                                      Total Alkali  3.51   3.36   3.38   3.64                                       % CaCl.sub.2  0.50   0.59   0.57   0.83                                       % NaCl        16.51  16.38  15.87  16.53                                      % Ca(ClO.sub.3).sub.2                                                                       1.33   1.13   1.28   1.38                                       % CaCO.sub.3  2.31   1.93   2.36   2.43                                       Packed bulk Density (g/cc)                                                                  1.08   1.08   1.06   1.08                                       % Screen Analysis                                                             Mesh   Microns                                                                +20    > 850  61.42  63.95  65.88  62.20                                      -20 to +50                                                                           850 to 300                                                                           37.02  34.57  33.20  39.45                                      -50    <300   1.34   1.53   0.98   1.33                                       __________________________________________________________________________

Five grams of the commercial granular hydrated calcium hypochlorite ofthe above compositions were dispersed daily in the tank using the exactprocedure of EXAMPLE 1 for the same time period. The average percent ofcommercial hydrated Ca(OCl)₂ particles which dissolved is shown in TableI below.

                  TABLE I                                                         ______________________________________                                        Hydrated Ca(OCl).sub.2 Particles Dissolved                                    Example                                                                              % Particles                                                                             Comparative                                                                              % Particles                                       No.    Dissolved Example    Dissolved                                                                             % Difference                              ______________________________________                                        1      72.6      A          49.1    23.5                                      2      74.5      B          50.0    24.5                                      3      75.9      C          51.2    24.7                                      4      76.8      D          52.3    24.5                                      ______________________________________                                    

Using the improved granular hydrated calcium hypochlorite product of thepresent invention, there was an average increase in the solubility rateof at least 23 percent over that of the commercial granular hydratedcalcium hypochlorite of the prior art.

What is claimed is:
 1. A rapidly dissolving granular hydrated calciumhypochlorite product consisting essentially of hydrated calciumhypochlorite particles having at least 95 percent of said particleswithin a size range of from about 300 to about 850 microns and having apacked bulk density from about 0.90 to about 1.03 grams per cubiccentimeter.
 2. The granular hydrated calcium hypochlorite product ofclaim 1 in which the hydrated calcium hypochlorite particles have awater content of from about 5 to about 8 percent and an availablechlorine content of from about 55 to about 75 percent.
 3. The granularhydrated calcium hypochlorite product of claim 1 in which the particlesize range is from about 325 to about 800 microns.
 4. A rapidlydissolving calcium hypochlorite product, consisting essentially ofgranular hydrated calcium hypochlorite having an available chlorineconcentration of from about 65 to about 72 percent, and having a packedbulk density from about 0.90 to about 1.03 grams per cubic centimeterand having a dissolving rate of about 70 weight percent or higher in oneminute when dispersed on the surface of a body of water at least 3 feetdeep, at least 95 percent of said particles having a size range of fromabout 300 to about 850 microns.
 5. The granular hydrated calciumhypochlorite product of claim 4 having at least 97% of the particleswithin a size range of from about 300 to about 850 microns.